1. Technical Field
The invention relates to a system for regulation of the output power of a transmitter, in particular of a radio-frequency transmitter.
2. Background Information
Relatively large fluctuations may occur in the process parameters during the process of producing semiconductor components using CMOS technology. This variation may lead to severe fluctuations in the component characteristics of CMOS semiconductor components. For power amplifiers produced using CMOS technology, this leads to considerable variations in the output power. In this case, power differences of several dB typically occur particularly in radio-frequency transmitters, in which a modulated and amplified, radio-frequency transmission signal is produced from a modulation signal.
In addition, the characteristics of the semiconductor components vary based on temperature fluctuations, and for amplifiers, this leads to additional fluctuations in the output power. Analog controllers may be used to compensate for the temperature-dependent fluctuations of the component characteristics. However, CMOS semiconductor components have a highly complex temperature response, which necessitates a high degree of complexity to achieve satisfactory results. Furthermore, a controller such as this does not allow compensation for the fluctuations in the component characteristics that are caused by the production process.
In addition, a control loop may be provided in which the output power of an amplifier is measured, and its input signal regulated. If the load at the output of the amplifier is formed by a load which is not specified in any more detail, such as an unmatched antenna, then special precautions are required to reduce reaction effects on the power measurement, and these can lead to corrupted measurement results. By way of example, a directional coupler is required for this purpose, which must be arranged externally, that is to say not within the integrated circuit. This type of power measurement thus increases the number of components, which results in an increased space requirement, an increased current drawn by the overall apparatus, and in increased production costs.
A further option for compensation for the fluctuations in the component characteristics caused by the production process is to measure each transmission circuit individually after production, and to calibrate it in accordance with the measurement results. This option is not practicable, because of the excessively high costs.